A. Field of the Invention
The present invention relates to elongate structural members having W-shaped cross-sections with a rounded, circular appearance and a generally circular outline. More particularly, the preferred structural members of the present invention are manufactured from fiber-reinforced plastics. The structural members of the present invention are useful in wheelchairs, particularly as wheelchair push handles and wheelchair cross-brace seat support members. The inventive concept may be incorporated into many different physical configurations, however. Some embodiments of the invention also include stiffening disks for limiting the amount of torsional movement and bending the structural member is capable of.
B. Related Art
For the purposes of this patent, the types of movement of elongate members are discussed. The first is longitudinal displacement, or displacement along the longitudinal axis of a structural member. Longitudinal displacement is usually found in soft materials such as rubber. The second is torsional movement, or twisting about the longitudinal axis of the member. The third is bending along the longitudinal axis of the structural member, or deflection of a portion of the structural member away from its longitudinal axis. Many structural members are stiff tubular members which have little or no torsional or bending ability. Such structural members are not capable of sufficient flexion or torsional movement for many applications. Thus, those structural members lack adequate shock absorbing characteristics for many applications.
Many light weight structural members in the prior art are expensive to manufacture. This is especially true of many wheelchair structural members. For example, when aluminum tubing is used to make wheelchair push handles, the aluminum must be bent and machined. Filament winding, composite lay up and some other methods for forming composite products are also undesirable since they are generally time consuming and expensive. Similarly, the manufacture and assembly of multiple parts tends to be more labor intensive and expensive than the manufacture and assembly of fewer parts. In comparison, the preferred wheelchair push handles of the present invention cost about sixty percent (60%) or less to manufacture than similar parts made from aluminum tubing. When compared with similar parts made by filament winding or composite lay up, products made in accordance with the preferred configuration and methods of the present invention represent even greater manufacturing cost savings.
The following U.S. Patents, which disclose structural or strengthening members with a W-shaped cross-section, may also be of interest to the reader: U.S. Pat. Nos. 5,595,800, issued in the name of Stanley W. O. Menzel; 5,560,672, issued in the names of George G. Lim, Clifford C. Chow and Alan A Kinnelly; 5,415,301, issued in the names of John Bruton and Julian De Salis; 5,295,446, issued in the name of Gerhard Schafer; 5,291,716, issued in the names of Peter O. Broberg, Find Madsen and Jorgen H. Christensen; and 4,351,244, issued in the name of James M. Suttles; 3,768,423, issued in names of James M. Cook, III and Eugene Dow.
The '800 patent describes a flexible reinforcing member for strengthening helically wound composite structures. The '672 patent discloses a structural member with hinge points that facilitate plastic deformation of the member. The '301 patent discloses a structural member having opposing sides which each have a W-shaped cross-section. The '446 patent describes hollow shelf posts with a W-shaped cross-section. The '716 patent describes a structural assembly for constructing buildings which includes a sectional element having a W-shaped cross-section. The '244 patent discloses a shelving system with corner posts having a W-shaped cross-section. The '423 patent discloses a pallet having strengthening ribs with a W-shaped cross-section.
Each of these patents describes strengthening or structural members having a W-shaped cross-section with flat members which join at angular comers. Thus, the structural members described in those patents are more likely to collapse under transverse side loads than prior art tubular members and the structural members of the present invention. None of these patents discloses a W-shaped cross-section which has a rounded cross-sectional outline. Thus, such structural members cannot be easily integrated into many apparatus to replace existing tubular parts. Nor does any of the patents describe the use of a mechanism for controlling the amount of torsional and bending movement of which the structural member is capable.
Torsional and bending movement is sometimes a desirable feature in structural members. Consequently, such structural members have the ability to absorb shock from a transverse impact. Such pylons include flat elongate members, elongate members with a U-shaped cross-section, and the use of two or more elongate members of different thicknesses. However, the amount of torsion and bending of many of those structural members cannot be controlled.
The following U.S. Patents, which disclose prosthetic pylons, represent some of the structural members which are capable of torsional and bending movement. U.S. Pat. No. 4,959,073, issued in the name of John Merlette, discloses a flat elongate member which includes a layer of diagonally oriented fibers on at least the front and back surfaces thereof. The layer of diagonal fibers provides torsional stiffness control and stability to the pylon.
While the prosthetic pylon described by the '073 patent may be capable of torsional rotation and has some flexibility, the use of a flat member may generate too much torsion and flexion for many users. Further, the torsional stiffness of that pylon is controlled only by variation of the materials used in the manufacture thereof.
U.S. Pat. No. 4,547,913, issued in the name of Van L. Phillips, describes a prosthetic foot and leg having a flat, elongate pylon. The leg of the '913 patent is formed from a synthetic resin impregnated high strength filament. The '913 patent discloses the ability of that pylon to rotate under torsional stress. However, no mechanisms are disclosed for tailoring the amount of torsion or flexion of which that pylon is capable to the needs of particular users.
U.S. Pat. No. 4,822,363, issued in the name of Van L. Phillips, discloses a modular prosthetic leg which has a generally flat, elongate pylon. This shape facilitates torsional rotation of the pylon. The preferred embodiment of the pylon of the '363 patent fabricated from filamentary laminates. Various embodiments of the pylon provide the desired characteristics for a wide range of users' weights and activity levels. However, the various embodiments merely include alternatives on the size of the pylon and the materials used to manufacture the pylons.
U.S. Pat. No. 5,156,631, issued in the name of John Merlette, describes a foot and leg prosthesis having a pylon, or shank strut section, having a U-shaped cross-section. The '631 patent notes that the U-shaped cross-section, in combination with the use of a unidirectional fiberglass composite, provides bending stiffness. The preferred use of cross-plied woven fabric at the surface of the pylon also imparts it with torsional stiffness.
However, as with the pylons having elongate flat members, the U-shaped cross-section pylon of the '631 patent may have too much torsion and flex for many users. The '631 patent also lacks disclosure about mechanisms for controlling the stiffness of the pylon structural member.
U.S. Pat. Nos. 5,217,500 and 5,464,441, both issued in the name of Van L. Phillips, each disclose a prosthetic leg pylon having at least one elongate leg element which is capable of responding to stress. Mr. Phillips prefers that the pylon include two elongate leg elements which are attached to one another. A spacer may also be attached between the leg elements. Both the '500 patent and the '441 patent note that the use of more than one leg element provides a pylon with more flexibility than single element pylons of equivalent cross-sectional area. The use of multiple elongate elements and spacers is undesirable since it increases manufacturing costs significantly.
U.S. Pat. No. 5,314,499, issued in the name of Milo S. Collier, Jr., discloses a prosthesis which includes, among other things, a shin having two rods. Mr. Collier prefers that the rods have some flexiblity and different diameters in order to represent the tibia and fibula of the human lower leg. The configuration and flexibility of the rods impart the shin with the ability to twist and flex slightly. Again, the use of multiple pieces creates a significant increase in manufacturing cost.
3 U.S. Pat. No. 5,509,936, issued in the names of Albert Rappoport and Jerome P. Voisin, describes a leg prosthesis having a dual leaf spring configuration. The flat, elongate leaf springs are curvilinear, and are positioned such that they bow away from one another. This leaf spring configuration facilitates torsional movement of the leg, along with compression and flexion of the prosthetic leg in the fore and aft directions. However, the multiple pieces of the pylon of the '936 patent significantly increase its cost of manufacture over single-member pylons. Further, compression is often undesirable in prosthetic pylons since natural limbs have little or no compressibility.
Applicants are aware of several prior art wheelchairs. For a general background concerning wheelchairs, wheelchair componentry and related componentry, the reader is directed to the following U.S. Pat. Nos. Re. 32,242, issued in the name of Minnebracker; D. 306,712, issued in the name of Friedrich; 2,425,574, issued in the name of Stewack; 2,824,597, issued in the name of Lerman; 3,356,185, issued in the name of Isaacks; No. 3,618,968, issued in the name of Green; 3,897,857, issued in the name of Rodaway, 3,901,527, issued in the names of Danziger et al.; 3,964,786, issued in the name of Machuda; 4,280,595, issued in the names of Timms et al.; 4,431,076, issued in the name of Simpson; 4,489,955, issued in the name of Hamilton; 4,500,102, issued in the names of Haury et al.; 4,501,033, issued in the names of Kessel et al; 4,593,929, issued in the name of Williams, 4,598,944, issued in the name of Meyer, 4,652,005, issued in the name of Hartwell; 4,733,755, issued in the name of Manning; 4,768,797, issued in the name of Friedrich; 4,953,913, issued in the name of Graebe; 4,989,890, issued in the name of Lockard; 5,028,065, issued in the name of Danecker; 5,060,962, issued in the name of McWethy; 5,074,620, issued in the names of Joy et al.; 5,120,071, issued in the name of Thibault; 5,152,543, issued in the names of Sims et al.; 5,176,393, issued in the name of Robertson; 5,203,433, issued in the name of Dugas; 5,242,179, issued in the names Beddome et al.; 5,249,847, issued in the name of Lee; 5,253,888, issued in the name of Friedrich; 5,379,866, issued in the names of Pearce et al.; and 5,603,520, issued name of Pearce.
Applicants are also aware of several prior art structural members which are manufactured from molded plastic materials, including frame members for wheelchairs and bicycles. For a general background of such structural members, the reader is directed to the following U.S. Pat. Nos. 3,533,643, issued in the name of Yamada; 4,067,589, issued in the name of Hon; 4,548,422, issued in the names of Michel et al.; 4,550,927, issued in the name of Resele; 4,593,929, issued in the name of Williams; 4,865,337, issued in the name of Disler; 5,011,172, issed in the names of Bellenca et al.; 5,092,614, issued in the name of Malewicz; 5,253,888, issued in the name of Friedrich; and 5,464,240, issued in the names of Robinson et al. French patent no. 895046, Italian patent no. 448310 and United Kingdom patent no. 191193, issued in 1895, may also be of interest to the reader.
What is needed is a rigid structural member which i is relatively inexpensive to manufacture, preferably by injection molding of a fiber reinforced material. A mechanism is needed for imparting torsional and bending stiffness to the structural member. A structural member which may be readily integrated into existing apparatus designs is needed. A structural member is also needed which resists compression and absorbs transverse shocks. The prior art does not fill these needs.